Fish do not hear the pings or chirps. your sonar ping, listen, ping, listen.. etc. in real time that is about 20000 times a second!
the theory is a bunch of boats fishing. the fish scatter. people think its the ping. Its not, its all the commotion in the boats, shadows, and his buddy that suddenly disappears, and the ping of the keystone light like natahka72 said..
For perspective a ping ( like a peep, peep, peep, of a chick ) or a chirp (like a long whistle)
verticle noise is from other sonar (verticle noise is straight lines, faint to heavy.)
Noise from trolling motor...Ferrite rings are the magic bullet to eliminate that. very simple and free.
If you have a weed screen on the back of your lund livewell intake you are probably interfering with your side image.